Gripper feeder for metal strip

ABSTRACT

A gripper feeder for metal strip including on a base one pair of grippers for an engagement of a metal strip to be advanced; members for moving said grippers in a direction parallel to an axis of the strip and in the opposite direction; and means for independently operating the grippers such that the gripper which moves in the direction of advancement of the strip is activated, whereas that which moves in an opposite direction is deactivated.

FIELD OF THE INVENTION

This invention relates to a gripper feeder for metal strip.

DESCRIPTION OF THE PRIOR ART

Metal strip feeders are known for presses and machines in general inwhich the strip is subjected to particular operations as required.

A known type of feeder of pneumatic operation uses two clamps actingtransversely on the strip to be conveyed. One of these clamps is fixed,while the other is driven with reciprocating movement in a directionparallel to the longitudinal axis of the strip. In operation, the twoclamps are operated alternately in a synchronized manner in the sensethat when the fixed clamp is open the mobile clamp is closed onto thestrip to advance it, whereas on termination of the advancement stroke ofthe mobile clamp the fixed clamp is closed and, after being opened, themobile clamp is returned backwards to grip the metal strip furtherupstream and then advance it through a further distance when the fixedclamp is reopened.

A drawback of this known feeder is that it is non-continuous and doesnot enable high operating speeds to be achieved.

A further drawback is that it is extremely rigid, in the sense that itrequires laborious manual action each time the advancement pitch of themetal strip is to be modified.

A further drawback is that as it moves the metal strip by thrusting, itcannot be used for very thin strip.

A further drawback is that it occupies the entire surface of the stripto be conveyed and does not allow it to be operated upon in that partengaged by the feeder.

A further drawback is that it has a transverse dimension greater thanthe width of the strip, and for certain strip widths this dimensionbecomes excessive.

A further drawback is that it cannot produce an advancement pitchgreater than certain length.

A roller feeder is also known comprising at least one pair ofcounter-rotating rollers between which the metal strip to be advanced isinterposed. It substantially overcomes the drawbacks of known pneumaticfeeders, and in particular is of continuous programmable operation.However it has other drawbacks, and in particular:

it engages the entire metal strip and therefore does not enable it to besubjected to other operations during the gripping;

it maintains the strip constantly engaged, and if this is curved in thehorizontal plane or is inserted incorrectly into the feeder, transversestresses of a progressively increasing extent arise and can beeliminated only by periodically slackening the grip between the rollers;

if the strip advancement is controlled by acting on the rollers, errorscan arise because of the inevitable slippage between the rollers and thestrip; if however it is controlled by acting on the strip itself theseerrors are not present, but the feeder then has a low advancement speedbecause of the need to correct errors deriving from inevitable slippage.

Mechanical feeders with grippers controlled by the power machinepositioned downstream of them are also known. In this case the grippersare driven with reciprocating movement and are reliable and fast.However they are extremely rigid in their performance and involve slowand difficult adjustment, which can be effected only by specializedpersonnel. EP-A-4874456 describes a method and device for advancing aband, in which the stepwise transport of the band is performed by twogrippers which are moved backwards and forward synchronously, each intheir longitudinal direction by a common drive.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is to provide a feeder:

which is sustantially continuous;

which does not engage the entire surface of the metal strip andtherefore enables it to be subjected to operations during its conveying;

which is fast;

which is programmable;

which is free from errors.

All these objects and further ones are attained according to theinvention through a gripper feeder for metal strip comprising on a base:

at least one pair of grippers for the engagement of the metal strip tobe advanced;

members for moving said grippers in a direction parallel to the axis ofsaid strip and in the opposite direction; and

means for independently operating said grippers such that the gripperwhich moves in the direction of advancement of the strip is activated,whereas that which moves in the opposite direction is deactivated, saidmembers for moving said grippers consisting of a rod engaged with athreaded bush provided on the grippers, and rotated by a single electricmotor powered alternately in the two directions of rotationcharacterized in that said rod has two portions threaded in oppositedirections.

BRIEF DESCRIPTION OF THE DRAWINGS

Two preferred embodiments of the present invention are further describedhereinafter by way of non-limiting example with reference to theaccompanying drawings, in which:

FIG. 1 is a longitudinal section of a first embodiment of a gripperfeeder according to the invention;

FIG. 2 is an enlarged cross-section therethrough on the line II--II ofFIG. 3;

FIG. 3 is a plan view thereof;

FIG. 4 is a longitudinal section of a second embodiment thereof;

FIG. 5 is an enlarged cross-section therethrough on the line V--V ofFIG. 5; and

FIG. 6 is a plan view.

DESCRIPTION OF PREFERRED EMBODIMENTS

As can be seen from the drawings, the gripper feeder for metal stripaccording to the invention comprises, in the embodiment shown in FIGS. 1to 3, a base 2 on which there are mounted two longitudinal rails 4,4'for guiding two slides 6,6' on which two carriages 8,8' are mounted.Each of the carriages 8,8' is provided with a threaded bush 10,10' inwhich there engages a threaded rod 12, provided with two portionsthreaded in opposite directions.

The threaded rod 12, is supported by a pair of supports 14,14' fixed tothe base 2. Specifically, each rod 12, is supported by the support 14exactly at its right hand end with reference to FIGS. 1 and 3, whereasit extends beyond the support 14' at its left hand end, to engage theexit shaft 22 of a direct current electric motor 24 mounted on the base2.

Each carriage 8,8' supports a gripper 26,26' which is slidable along adovetail rail 28,28' arranged transversely, ie perpendicular to the axisof the threaded rods 12, and of which the movements are controlled by arespective mechanical actuator 30,30'.

Each gripper 26,26' comprises a fixed jaw rigid with the slide slidablealong the corresponding rail 28,28', and a movable jaw 32,32' drivenrelative to the fixed jaw by a pneumatic actuator 34,34' of verticalaxis.

On the supports 14,14' for the threaded rods 12, there are also mountedtransverse dovetail guides 36,36' along which there slide pairs ofcarriages 38,38' supporting rollers 40,40' of vertical axis with theirlateral surface comprising a groove for engaging and guiding thelongitudinal edge of the metal strip 42 to be advanced.

The carriages 38,38' are driven along the respective guides 36,36' bymechanical actuators 44,44'.

The operation of this first embodiment of the feeder according to theinvention is as follows:

an adjustment is firstly made to adapt the machine to the width of thestrip 42 to be fed; this adjustment requires operating the actuators30,30' which adjust the distance between the grippers 26,26', and thenthe actuators 44,44' which adjust the distance between the guide rollers40,40' of each pair.

Having made this preliminary adjustment, the machine is ready tooperate. The electric motor 24 is powered to rotate in one of the twodirections of rotation, with the result that because of the particularcoupling between this latter and the two threaded rods 12, this isrotated in the same direction. However, as their threads are in oppositedirections, its rotation causes the two carriages 8,8' to slide in theopposite direction along the respective rails 4,4', with consequentsliding in the opposite direction of the two grippers 26,26' mounted onsaid carriages. At the same time an activation command is fed to thegripper 26, which during this stage moves in the same direction as thepredetermined direction of advancement of the metal strip 42, indicatedby the arrow 46 in the drawings, and a deactivation command is fed tothe gripper 26' which moves in the opposite direction.

When the gripper 26 has practically reached its front end-of-travelposition along the respective guide 4 and the gripper 26' has reachedits rear end-of-travel position along the respective guide 4', thedirection of rotation of the electric motor 24 is reversed while at thesame time a deactivation command is fed to the actuator 34 of thegripper 26 and a deactivation command is fed to the actuatore 34' of thegripper 26', so that also in this case the gripper which moves in thesame direction as the predetermined direction of advancement of themetal strip 42 grips said strip and the gripper which moves in theopposite direction disengages from it.

This alternation in the direction of rotation of the motor 24 and thealternation in the activation commands for the two grippers results inunidirectional advancement of the metal strip 42, this advancementhaving an intermittency which can be made to approach continuity bysuitably controlling the various intervention times.

From the aforegoing it is apparent that the gripper feeder according tothe invention is considerably more advantageous than conventionalfeeders, and in particular:

it grips the strip only along a longitudinal edge thereof, this on theone hand leaving the remainder of the strip free for possible operationsand on the other hand resulting in a small overall size independent ofthe strip width;

it grips the strip at successive points, so allowing any incorrectdragging due to strip curving or to incorrect insertion into the feederto be corrected;

it provides effective guide action for the strip along both edges;

it ensures reliable gripping of the metal strip 42 without any slippagebetween this and the grippers, so ensuring its correct advancement bycontrolling the motor 24 which operates the threaded rods 12,12'; inthis manner, electronic and hence programmable advancement control ismade possible in a like manner to conventional electronic rollerfeeders, while at the same time mechanical and hence slippage-freegripping is provided in a like manner to mechanical or pneumaticfeeders.

In the embodiment shown in FIGS. 4 to 6, two transverse grippers 126,126' are provided acting on the entire length of the metal strip 142.The lower jaw of each gripper 126, 126' lowerly protrudes in a carriage108, 108' provided with a threaded bush 110, 110' in which there engagesa threaded rod 112 realized in two portions threaded in oppositedirections.

The threaded rod is driven, as in the embodiment of FIGS. 1-3, by adirect current electric motor 124.

Each gripper comprises a fixed jaw rigid with the carriage and a movablejaw 123, 123' driven relative to the fixed jaw by pneumatic actuator134,134' of vertica axis.

It being understood that the general principle of gripping the metalstrip by a gripper which is kept engaged during the working stroke andopened during the return stroke, it is obvious that, due to the oppositethreads of the rods 112, while a gripper 126,126' carries out theworking stroke, the other gripper 126',126 carries out the returnstroke.

This embodiment enables to obtain a more reliable operative precisionsince the operating obtained through one threaded rod eliminates thepossible plays.

Furthermore the entire width shaped gripper enables to be adapted tometal strip of different width without however laterally adjusting theposition of the grippers.

I claim:
 1. A gripper feeder for a metal strip comprising:a base; guidemeans for guiding at least one pair of carriages slidable along saidguide means; a gripper mounted on each carriage of said at least onepair of carriages, for engagement of said metal strip to be moved;members for moving said gripper in a first direction of movementparallel to a longitudinal axis of said strip and in a second directionof movement opposite to said first direction; means for independentlyoperating said gripper of said at least one pair of carriages such thatwhen said gripper of one of said at least one pair of carriages moves insaid first direction of movement of said strip and is activated, agripper of a second carriage of said at least one pair carriages movesin said second opposite direction and is deactivated, said members formoving said at least one pair of carriages includes a single threadedrod and a single electric motor, which rotates said threaded rod, saidmotor being powered alternately in said first and second directions,wherein said rod has a first portion and a second portion threaded inopposite directions, a threaded bush provided on one carriage of said atleast one pair of carriages engaging said first portion and a threadedbush provided in said second carriage of said at least one pair ofcarriages engaging said second portion.
 2. A feeder as claimed in claim1 wherein said gripper of said at least one pair of carriages ispositioned on both sides of said metal strip.
 3. A feeder as claimed inclaim 1 wherein said gripper of said at least one pair of carriagesextends at least for an entire width of said strip.
 4. A feeder asclaimed in claim 1 wherein said gripper comprises a fixed part rigidwith said respective carriage and a movable part operated by anactuator.
 5. A feeder as claimed in claim 1 wherein said gripper ismounted on a slide slidable along a horizontal guide rail arrangedperpendicular to said axis of said metal strip.
 6. A feeder as claimedin claim 5, wherein an actuator is associated with said gripper formoving said gripper along said respective guide rail.
 7. A feeder asclaimed in claim 1, wherein on said base there are applied pairs ofrollers of vertical axis having in their lateral surface acircumferential groove for engaging and guiding a correspondinglongitudinal edge of said metal strip.
 8. A feeder as claimed in claim 7wherein at least one roller of each pair is movable relative to saidbase in a direction perpendicular to said axis of said metal strip.
 9. Afeeder as claimed in claim 8, wherein said two rollers of each pair aremounted on slides movable along a guide rail arranged perpendicular tosaid axis of said metal strip on supports rigid with said base.
 10. Afeeder as claimed in claim 9, wherein an actuator is interposed betweensaid slide of each guide roller and said respective support.